Depending on which pi you use you need around 0.5 to 1.5 amps for the pi. Remember the pi runs on 5v. You could easily for testing purposes run the board with just the pi on 16v AC. (Not DC). Solenoids all run on 24vac so you should get 24vac transformer for the final product. You could easily run a system including 1 solinoid at a time with a 1 amp. 24vac transformer.

Depending on which pi you use you need around 0.5 to 1.5 amps for the pi. Remember the pi runs on 5v. You could easily for testing purposes run the board with just the pi on 16v AC. (Not DC). Solenoids all run on 24vac so you should get 24vac transformer for the final product. You could easily run a system including 1 solinoid at a time with a 1 amp. 24vac transformer.

On the RPi power supplies.

-The RPi A/B/B+ all use the 5V /2A power supply units. Obviously, if you have extra boards attached to the RPi, like a HAT, you would need more current supplied. I'm currently using my RPi B with a hifi-berry dac running off the 5V/3A power supply.-From the RPi 3B/B+ you require the 5.1V/2A power supply units. -Here I would recommend buying the original RPi power supply, because of the voltage difference. I bought a 5V/3A power supply unit for my RPi and works, but gives the low voltage square when you run the RPi 3. Not a problem, as per say, just irritating.